Electrical connectors are used in many electronic systems. It is generally easier and more cost effective to manufacture a system on several printed circuit boards that are then joined together with electrical connectors. A traditional arrangement for joining several printed circuit boards is to have one printed circuit board serve as a backplane. Other printed circuit boards, called daughter boards, are connected through the backplane.
A traditional backplane is a printed circuit board with many connectors. Conducting traces in the printed circuit board connect to signal pins in the connectors so signals may be routed between the connectors. Daughter boards also contain connectors that are plugged into the connectors on the backplane. In this way, signals are routed among the daughter boards through the backplane. The daughter cards often plug into the backplane at a right angle. The connectors used for these applications contain a right angle bend and are often called xe2x80x9cright angle connectors.xe2x80x9d
Connectors are also used in other configurations for interconnecting printed circuit boards, and even for connecting cables to printed circuit boards. Sometimes, one or more small printed circuit boards are connected to another larger printed circuit board. The larger printed circuit board is called a xe2x80x9cmother boardxe2x80x9d and the printed circuit boards plugged into it are called daughter boards. Also, boards of the same size are sometimes aligned in parallel. Connectors used in these applications are sometimes called xe2x80x9cstacking connectorsxe2x80x9d or xe2x80x9cmezzanine connectors.xe2x80x9d
Regardless of the exact application, electrical connector designs have generally needed to mirror trends in the electronics industry. Electronic systems generally have gotten smaller and faster. They also handle much more data than systems built just a few years ago. These trends mean that electrical connectors must carry more and faster data signals in a smaller space without degrading the signal.
Connectors can be made to carry more signals in less space by placing the signal contacts in the connector closer together. Such connectors are called xe2x80x9chigh density connectors.xe2x80x9d The difficulty with placing signal contacts closer together is that there is electromagnetic coupling between the signal contacts. As the signal contacts are placed closer together, the electromagnetic coupling increases. Electromagnetic coupling also increases as the speed of the signals increase.
In a conductor, electromagnetic coupling is indicated by measuring the xe2x80x9ccross talkxe2x80x9d of the connector. Cross talk is generally measured by placing a signal on one or more signal contacts and measuring the amount of signal coupled to the contact from other neighboring signal contacts. In a traditional pin in box connector mating in which a grid of pin in box matings are provided, the cross talk is generally recognized as a sum total of signal coupling contributions from each of the four sides of the pin in box mating as well as those located diagonally from the mating.
A traditional method of reducing cross talk is to ground signal pins within the field of the signal pins. The disadvantage of this approach is that it reduces the effective signal density of the connector.
To make both a high speed and high density connector, connector designers have inserted shield members in proximity to signal contacts. The shields reduce the electromagnetic coupling between signal contacts, thus countering the effect of closer spacing or higher frequency signals. Shielding, if appropriately configured, can also control the impedance of the signal paths through the connector, which can also improve the integrity of signals carried by the connector.
An early use of shielding is shown in Japanese patent disclosure 49-6543 by Fujitsu, Ltd. dated Feb. 15, 1974. U.S. Pat. Nos. 4,632,476 and 4,806,107, both assigned to ATandT Bell Laboratories, show connector designs in which shields are used between columns of signal contacts. These patents describe connectors in which the shields run parallel to the signal contacts through both the daughter board and the backplane connectors. Cantilevered beams are used to make electrical contact between the shield and the backplane connectors. U.S. Pat. Nos. 5,433,617; 5,429,521; 5,429,520 and 5,433,618, all assigned to Framatome Connectors International, show a similar arrangement. The electrical connection between the backplane and shield is, however, made with a spring type contact.
Other connectors have the shield plate within only the daughter card connector. Examples of such connector designs can be found in U.S. Pat. Nos. 4,846,727, 4,975,084, 5,496,183 and 5,066,236, all assigned to AMP, Inc. Another connector with shields only within the daughter board connector is shown in U.S. Pat. No. 5,484,310, assigned to Teradyne, Inc.
A modular approach to connector systems was introduced by Teradyne Connection Systems, of Nashua, New Hampshire. In a connector system called HD+(copyright), multiple modules or columns of signal contacts are arranged on a metal stiffener. Typically, 15 to 20 such columns are provided in each module. A more flexible configuration results from the modularity of the connector such that connectors xe2x80x9ccustomizedxe2x80x9d for a particular application do not require specialized tooling or machinery to create. In addition, many tolerance issues that occur in larger non-modular connectors may be avoided.
A more recent development in such modular connectors was introduced by Teradyne, Inc. and is shown in U.S. Pat. Nos. 5,980,321 and 5,993,259 which are hereby incorporated by reference. Teradyne, Inc., assignee of the above-identified patents, sells a commercial embodiment under the trade name VHDM(trademark).
The patents show a two piece connector. A daughter card portion of the connector includes a plurality of modules held on a metal stiffener. Here, each module is assembled from two wafers, a ground wafer and a signal wafer. The backplane connector, or pin header, includes columns of signal pins with a plurality of backplane shields located between adjacent columns of signal pins.
Yet another variation of a modular connector is disclosed in patent application Ser. No. 09/199,126 which is hereby incorporated by reference. Teradyne Inc., assignee of the patent application, sells a commercial embodiment of the connector under the trade name VHDM-HSD. The application shows a connector similar to the VHDM(trademark) connector, a modular connector held together on a metal stiffener, each module being assembled from two wafers. The wafers shown in the patent application, however, have signal contacts arranged in pairs. These contact pairs are configured to provide a differential signal. Signal contacts that comprise a pair are spaced closer to each other than either contact is to an adjacent signal contact that is a member of a different signal pair.
As discussed in the background, higher speed and higher density connectors are required to keep pace with the current trends in the electronic systems industry. With these higher densities and higher speeds however electromagnetic coupling or cross talk between the signal contacts becomes more problematic.
An electrical connector having mating pieces with shields in one piece oriented transversely to the shields in a second piece is therefore provided. In a preferred embodiment, one piece of the connector is assembled from wafers with shields positioned between the wafers. The shields in one piece have contact portions associated therewith for making electrical connection to shield in the other piece. With such an arrangement, a connector is provided that is easily manufactured and possesses improved shielding characteristics.
In other embodiments, the second piece of the connector is manufactured from a metal and includes slots into which signal contacts surrounded by an insulative material are inserted. With such an arrangement, the signal contacts are provided an additional four-walled shield against cross talk.